Electric discharge lamp

ABSTRACT

A low pressure electric discharge lamp comprising a sealed light-transmissive envelope and a fill within the envelope; the fill including, as the primary light-emitting material, a highly fluorescent aromatic organic compound, such as perylene, coronene, p-terphenyl, 1,6-diphenyl-hexa-1,3,5-triene, 9,10diphenylanthracene, and 1,4-bis-2-(4-methyl-5-phenyloxazolyl) benzene. At operating temperatures, the pressure or partial pressure of the vaporized organic compound is less than 1 torr.

United States Patent [19] July 16, 1974 Pappalardo et al.

[ ELECTRIC DISCHARGE LAMP [75] Inventors: Romano G. Pappalardo, Sudbury,

Mass; Samir A. Ahmed, Manhattan,

21 1 Appl. No.: 356,521

Primary Examiner-Herman Karl Saalbach Assistant Examiner-Darwin R. Hostetter Attorney, Agent, or Firmlrving M. Kriegsman 5 7 ABSTRACT A low pressure electric discharge lamp comprising a sealed light-transmissive envelope and a fill within the envelope; the fill including, as the primary lightemitting material, a highly fluorescent aromatic organic compound, such' as perylene, coronene, p-

[52] US. Cl 312/225, 3 13/22?) terphenyl, p y [51] Int. Cl. H01J 61/12 di hen lanthracene and 1 4 2 th 15 58 Field of Search 313/223, 224, 225, 226 P y e phenyloxazolyl) benaene. At operating temperatures, [561 UNlTED STATES PATENTS g p 3,530,325 9/1970 Mehl et al 313/108 7 9 1 Drawing Figure I 2 j e,

L H EATER ELECTRIC DISCHARGE LAMP The invention herein described was made in the course of or under a contract or subcontract thereunder with the US. Navy.

BACKGROUND OF THE INVENTION This invention relates to low pressure electric discharge lamps. More particularly, this invention relates to low pressure electric discharge lamps having a highly fluorescent aromatic organic compound as the major trodes in such a lamp, the mercury is excited and emits its characteristic spectral lines principally in the ultraviolet and blue-green region of the spectrum. It has recently been discovered that these lamps could be modified in their spectral emission by the inclusion-of elements and compounds other than mercury, whereby the light produced is a combination of the emissions of mercury and the added material(s). Blending of emissions in this manner can produce wide variations in colors and, most importantly, an essentially white spectrum can be attained. Added materials which have been suggested include the rare earth metals, added either in the form of the metal per se or as its halide.

Many of the rare earth metals, when dissociated from the halogenin the arc of the discharge lamp, emit a dense line spectrum predominantly in the visible region. A high vapor pressure must be maintained in order to achieve such line emission. This vapor pressure is, itself, generally maintained by keeping the 000- lest part of the envelope near 900C.

It would be desirable to provide an electric discharge lamp which provides broad-band visible and ultraviolet emission from the primary light-emitting component of the fill, as opposed to the characteristic ?line emission as described above.

OBJECTS OF THE INVENTION It is, therefore, an object of the present invention to provide a novel electric discharge lamp.

It is a further object of the present invention to provide a novel electric discharge lamp which emits broadband emission from the primary light-emitting component of the fill.

It is a further object of the present invention to provide an electric discharge lamp having a novel fill.

It is a further object of the present invention to provide an electric discharge lamp which includes a fill whose primary component is a highly fluorescent, aromatic organic compound.

These and still further objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed disclosure.

BRIEF SUMMARY OF THE INVENTION 2 hexa-l,3,5-triene, 9,10-diphenylanthracene, and 1,4- bis-2-(4-methyl-5-phenyloxazolyl) benzene. At operating temperatures, the pressure or partial pressure of the aromatic organic compound is less than 1 torr, generally about O.l torr to about 0.5 torr.

Organic compounds previously added to the fills of electric discharge lamps are usually dissociated by electronic impact in arc discharges. This produces irreversible decomposition of the organic compound and, occasionally, light emission from the radical species produced during the dissociation process. Such emission is in the form of line or narrow-band emission, as opposed to the broad-band emission from the fill components of the present invention. Broad-band emission, as attained by the present invention, is by emission from the vaporized molecular species (i.e., the organic compound in the vapor phase), and should be understood to be different than dissociation of the organic compound and emission from a dissociated product, atom, or radical species thereof. The discharge conditions, in particular the choice of buffer gas and of its pressure, are such to minimize the decomposition of the organic constituent:

The fill also includes a conventional quantity of an inert or noble gas, such as argon, helium, neon or xenon, preferably argon, from about 5 to about 25 torr, to facilitate starting. In addition, mercury can be added if desired, for example, in an amount which. will give a partial pressure of up to l torr or so at the operating temperature. Other well-known and conventional materials can be added to the fill, if desired, for their known purposes, e.g., to lower operating voltages, adjust spectral output, etc., if such addition does not adversely affect the broad-band emission attained with the vaporized organic compounds, as set forth above.

In the low pressure discharge lamps contemplated by this invention, the total pressure, at operating temperature, is of the order of about 5 torr to about 30 torr, with the substantial majority of such pressure resulting from' the noble gas, such as argon, added to the envelope to facilitate starting. As indicated above, the pressure or partial pressure (at operating temperature) of the vaporized organic compound is less than 1 torr, generally on the order of about 0.1 torr to about 0.5 torr. This can be achieved, for example, by adding sufficient organic compound to the envelope and running the discharge for a period of time sufficient to vaporize the desired quantity of the organic compound, or preferably, by providing heater means, such as a heater gun, heater tape, or heater filament (as shown by Thouret et al. US. Pat. No. 3,445,719) outside but in contact with, or closely adjacent, the envelope. As shown in the aforementioned Thouret et al patent, the heater filament can be positioned within the space between the inner envelope, containing the organic compound to be vaporized, and an outer envelope. Suitable operating temperatures, for example, are l20l50C for perylene and 2l5250C for coronene. For a conventional 400 watt envelope, having dimensions described below, a sufficient quantity of the organic compound is about 20-30 mg of the compound at cold fill. This represents a cold fill of about 1-2 mg of the organic compound per cc. of envelope volume.

The sealed light-transmissive envelope is generally made of quartz, although other types of glass may be used, such as pyrex, alumina glass or Vycor, the last being a glass of high silica content. It is essential, of course, that the material selected for the envelope and the materials utilized in the fill not adversely react with one another (either in the vaporized or non-vaporized state of the organic compound). Energizing means are provided for producing an electrical discharge inside the envelope. Typically, the energizing means is a neon-sign transformer whose output voltage is varied by changing the voltage in the primary. An a.c. milliammeter can be used to measure the current through the lamp. Typical operating currents vary from 0.3 mA to I.5' mA. The 'emission from the lamp can also be obtained in an electrodeless configuration, by exciting the discharge by means of the high-frequency voltage from a Tesla coil.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE is an elevation view of an electric discharge lamp constructed according to one embodiment of'the invention.

Referring to the sole FIGURE, discharge lamp includes a sealed light-transmissive envelope 12'having main discharge electrodes 13 and 14 at opposite ends thereof. Electrodes l3 and 14, made of a suitable metal such asthoriated tungsten, are supported on lead-in wires 15 and 16, respectively, and have tungsten helixes l7 and 18, respectively, at their interior ends. An auxiliary starting electrode 19, generally prepared of tantalum ortun gsten, is provided at one end of envelope 12 adjacent main discharge electrode 14, and comprises an inwardly projecting end of another leadinwire 20.

Each of the three current lead-in wires 15, 16 and 20 have their ends welded to intermediate foil sections 21, 22 and 23, respectively, of molybdenum which are hermetically sealed within.pinched sealed portions 24 and 25 of envelope 12. The foil sections are very thin, for example, approximately 0.0008 inch thick, and go into tension without rupturing or sealing off when the heated envelope cools. Molybdenum or tantalum wires 26, 27 and 28 are welded to the outer ends of foils 21, 22 and 23, respectively, and serve to convey current to the electrodes inside envelope 12. Inside envelope 12, there is volume 29 in which the organic compound herein described is volatilizedetc.'during operation of the lamp. I

In the embodiment of this invention where the fill is heated by external heater means, the disclosure of FIGS. 1-6, and those portions of the specification relating thereto,'of Thouret et al U.S. Pat. No. 3,445,719 is incorporated hereby by reference as showing exemplary structures suitable for use with the present inven- DESCRIPTION OF SPECIFIC EMBODIMENTS The following examples are given to enable those skilled in this art to more fully understand and practice the present invention. They should not be considered as a limitation upon the scope of the invention but merely as being illustrative and representative thereof.

In the following examples, the envelope utilized is a 400 watt quartz envelope having a diameter of about 2.3 cm., a length of about 6.0 cm., a distance between tungsten electrode tips of about 5.3 cm. and a volume of about 14.0 cc.

EXAMPLE I A 400 watt quartz envelope is filled with 20 mg. perylene and 12 torr argon. At room temperature, a potential difference of 7,000 volts from a non-sign transformer (60 Hz) excitation means gives a pale purple glow. At lamp envelope temperature of about C,

the perylene molecules vaporize, and the discharge is intensely blue and diffused over most of the envelope volume. A broad-band emission spectrum having a double peak at 419-424'nm, and similar doublets at 443-448 nm and 470-476 nm is obtained.

EXAMPLE II Example I is repeated except 10 torr helium'is substituted for the. 12 torr argon. A similar broadband emission spectrum is obtained, but the intensity is reduced approximately by a factor of S.

EXAMPLES m-v Example I is repeated except 4.5 torr argon, 1 0.5 torr argon, and 25 torr argon, respectively, are substituted for the 12 torr argon. Similar results are obtained.

EXAMPLE v1 Example I is repeated except about 30 mg. coronene is substituted for the perylene, and the partial pressure of the argon is 25 torr. When operated at 215C and 3,500 volts excitation (60 Hz), a broad band blue emission, having a peak at about 448 nm, is obtained.

EXAMPLES VII-VIII Example VI is repeated except 10 torr argon and I4 torr argon, respectively, are substituted for the 25 torr argon. Similar results are'obtained.

EXAMPLE IX EXAMPLE XI A 400 watt quartz envelope is filled with about 50 mg. l,6-diphenyl-hexa-l,3,5-triene and 10 torr argon. At lamp envelope temperature of about 180C and 4,200 volts excitation (60 Hz), a broad-band blue emission spectrum, having its peak at about 455 nm, is obtained.

I EXAMPLES XII-XIII A 400 watt quartz envelope is filled with 30 mg. 9,10-

diphenylanthracene and torr argon. When operated at about l42C and 5,000 volts excitation (60 Hz), a broad band purple-blue emission spectrum, having its peak at about 415 nm, is obtained. When 3.5 torr helium is substituted for the argon at constant temperature, the discharge is weak, more constricted, with strong emission lines being superimposed over the original broad band emission, which itself was decreased in intensity.

EXAMPLE XIV A 400 watt quartz envelope is filled with about 30 mg. of l,4-bis-2-(4-methyl-5-phenyloxazolyl) benzene and 15 torr argon. At lamp envelope temperature of about 200C a broad band blue emission spectrum is obtained.

While the present invention has been described with reference to specific embodiments thereof, it will be understood by those skilled in this art that various changes may be made without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, apparatus, process or then present objective to the spirit of this invention without departing from its essential teachings.

What is claimed is:'

l. A low pressure electric discharge lamp comprising a sealed light-transmissive envelope; and a fill within said sealed envelope, said fill including as the primary light-emitting component, a highly fluorescent, aromatic organic compound in a quantity sufficient to provide, at operating temperature, a partial pressure of said vaporized organic compound of less than about 1 torr; the discharge being characterized by substantially broad-band emission from said vaporized organic compound in the molecular state.

2. The lamp of claim 1 wherein said orgainc compound is perylene.

3. The lamp of claim 1 wherein said organic compound is coronene.

4. The lamp of claim 1 wherein said organic compound is p-terphenyl.

5. The lamp of claim 1 wherein said organic compound is LG-diphenyI-hexa l ,3 ,S-triene.

6. The lamp of claim 1 wherein said organic compound is 9,10-diphenylanthracene.

7. The lamp of claim 1 wherein said organic compound is l,4-bis-2-(4-methyl-5-phenyloxazolyl) benzene.

8. The lamp of claim 1 wherein said partial pressure of said organic compound is about 0.] torr to about 0.5 torr.

9. The lamp of claim 1 wherein said fill further includes a small quantity of a noble or inert gas to facilitate starting.

10. The lamp of claim 9 wherein said noble or inert gas is selected from the group consisting of argon, helium, neon or xenon. I

11. The lamp of claim 9 wherein said noble gas is argon.

12. The lamp of claim 9 wherein said noble or inert gas is present in an amount from about 5 torr to about 25 torr.

13. The lamp of claim 9 wherein said fill further includes a small quantity of mercury which, at operating temperature,- will generate a partial pressure ofup to about 1 torr.

14. The lamp of claim 1 further including heater means outside said envelope but closely adjacent thereto or in contact therewith, said heater means serving to assist in the vaporization of said organic compound to a temperature where said broad-band emission is attained.

15. The lamp of claim 14 wherein said temperature is on the order of about C to about 250C.

16. The lamp of claim 1 wherein the total pressure within said envelope, at operating temperatures, is up to about 30 torr.

17. The lamp of claim 1 further including a pair of electrodes spaced within said envelope and capable of being connected, at those portions thereof extending outside of said envelope, to means for applying an electrical potential thereto. 

2. The lamp of claim 1 wherein said orgainc compound is perylene.
 3. The lamp of claim 1 wherein said organic compounD is coronene.
 4. The lamp of claim 1 wherein said organic compound is p-terphenyl.
 5. The lamp of claim 1 wherein said organic compound is 1,6-diphenyl-hexa-1,3,5-triene.
 6. The lamp of claim 1 wherein said organic compound is 9,10-diphenylanthracene.
 7. The lamp of claim 1 wherein said organic compound is 1,4-bis-2-(4-methyl-5-phenyloxazolyl) benzene.
 8. The lamp of claim 1 wherein said partial pressure of said organic compound is about 0.1 torr to about 0.5 torr.
 9. The lamp of claim 1 wherein said fill further includes a small quantity of a noble or inert gas to facilitate starting.
 10. The lamp of claim 9 wherein said noble or inert gas is selected from the group consisting of argon, helium, neon or xenon.
 11. The lamp of claim 9 wherein said noble gas is argon.
 12. The lamp of claim 9 wherein said noble or inert gas is present in an amount from about 5 torr to about 25 torr.
 13. The lamp of claim 9 wherein said fill further includes a small quantity of mercury which, at operating temperature, will generate a partial pressure of up to about 1 torr.
 14. The lamp of claim 1 further including heater means outside said envelope but closely adjacent thereto or in contact therewith, said heater means serving to assist in the vaporization of said organic compound to a temperature where said broad-band emission is attained.
 15. The lamp of claim 14 wherein said temperature is on the order of about 120*C to about 250*C.
 16. The lamp of claim 1 wherein the total pressure within said envelope, at operating temperatures, is up to about 30 torr.
 17. The lamp of claim 1 further including a pair of electrodes spaced within said envelope and capable of being connected, at those portions thereof extending outside of said envelope, to means for applying an electrical potential thereto. 